The present invention relates generally to refrigeration systems. More particularly, the present invention relates to a method and apparatus for operating an evaporative condenser refrigeration system at a low condensing temperature.
In a typical evaporative condenser refrigeration system, the condenser capacity is generally selected based upon the highest wet bulb temperature occuring in the area of use of the refrigeration system, i.e., the condenser capacity is designed for the extreme condition. A compressor delivers working fluid, such as ammonia, to be condensed at a pressure generally in the range of 165 to 185 pounds per square inch. In order to artificially maintain this pressure at wet bulb temperatures considerably below the design condition, a mechanism for controlling condenser capacity is employed. This mechanism may include a device for regulating the speed, or operating time, of a fan for moving air over the evaporative condenser. Another control system regulates the flow of cooling water to nozzles which spray water upon coils of the evaporative condenser.
The prior systems have functioned satisfactorily and are acceptable if energy for driving a compressor to maintain the pressure of the working fluid at the predetermined high level is plentiful and inexpensive. However, with the increasing cost of energy a more economical refrigeration system is desirable.
It has been found that the highest wet bulb temperature within a region is considerably higher than the average wet bulb temperature on a yearly basis. However, in order to take full advantage of the annual average wet bulb temperature a different concept of refrigeration system operation is required. A refrigeration system having an evaporative condenser selected in accordance with the annual average wet bulb temperature produces a significant decrease in the amount of power required to operate the compressor. This decrease in the compressor power requirement is due primarily to a generally reduced compressor discharge pressure into the evaporative condenser. However, a system having a condenser designed for the average wet bulb temperature must also be capable of operating satisfactorily at the highest wet bulb temperatures.
Accordingly, it is an object of the present invention to provide method and apparatus for operating an evaporative condenser system in which the condensing temperature follows the prevailing wet bulb temperature.
It is a further object of the present invention to provide a method for selecting an evaporative condenser capacity based upon the average wet bulb temperature.
Still a further object of the present invention is to provide an energy efficient method of operating an evaporative condenser refrigeration system which utilizes a condenser selected in accordance with the average wet bulb temperature.
Additionally, it is an object of the present invention to ensure energy efficient operation of a compressor in an evaporative condenser refrigeration system by employing a compressor capacity control to ensure operation of the compressor at the lowest practical compressor horsepower.
These and many other objects are achieved by the present invention in a method of operating a refrigeration system including a compressor, a wet condenser, an evaporator, and a coolant circulating therethrough. The coolant flow to the evaporator is established at a fixed rate. The coolant temperature within the condenser, i.e., the condensing temperature, is permitted to follow the prevailing wet bulb temperature surrounding the condenser.
The method of operating an evaporative condenser refrigeration system according to the present invention further includes selecting a suitable condenser having a sufficient capacity for operation at the annual average wet bulb temperature of the locality of the refrigeration system. The evaporative condenser is operated at full capacity at all times during operation of refrigeration system. The condensing temperature of the working fluid in the condenser is permitted to follow the prevailing wet bulb temperature surrounding the condenser at the given time.
According to a further feature of the present invention the capacity of the compressor delivering the working fluid to the condenser is controlled to ensure operation of the compressor at the lowest practical compressor horsepower. Still further, separation between the low pressure portion and the high pressure portion of the system is maintained so that working fluid is delivered at constant pressure to an evaporator even though the condensing pressure varies with the condensing temperature which follows the prevailing wet bulb temperature.
A refrigeration system according to the present invention includes an evaporator, a compressor, a condenser having a coolant flow tube exposed to saturated ambient air, and a network interconnecting the evaporator, the compressor and the condenser through which a coolant flows. The condenser is sized for operation at the annual average wet bulb temperature of the locality and the temperature of the coolant in the condenser is permitted to follow the prevailing wet bulb temperature.
According to the preferred embodiment of the present invention, a controlled pressure receiver is arranged to receive condensed coolant from the condenser. A line delivers fluid from the receiver to the evaporator. The pressure is maintained constant within the receiver by selectively communicating the receiver with either the inlet to the compressor or the outlet from the compressor.